PET Scans and Diagnosis of Brain Injuries


In some cases, the downside of a misdiagnosis is not too serious. But when it comes to brain injuries, the risks of an incorrect diagnosis could mean the difference between dying or living, or the difference between the labels “vegetative state” and “minimally conscious.

We want our doctors to always be right. As patients, we want an exact diagnosis, a 100% effective treatment, and certainty about how long we’ll be sick. But medical diagnosis depends on a variety of factors, including the reliability of tests. Predicting the length and seriousness of a disease is an inexact science.  

An article in the British Medical Journal points out that “No tool exists for quantifying the extent of consciousness.” “Vegetative state” means the patient has no consciousness; she is completely unaware. The diagnosis is based on a detailed clinical history and careful observation of the patient who exhibits wakefulness, but not awareness.[1] This assumes that someone is conscious if they can indicate that they are aware. It’s possible that as many as 40% of patients who were diagnosed in a vegetative state, actually do have some degree of awareness.[2] Misdiagnosis has implications for managing the patient’s day-to-day care, how aggressively to intervene in the early days, and even how to talk in front of the patient.    

EEG scans may indicate signs of consciousness in a patient previously diagnosed as being in a vegetative state. But, a brand new study has shown that even EEGs can miss signs of consciousness. 126 patients with brain injuries including ‘unresponsive wakefulness syndrome’—another term for vegetative state—were examined using PET scans and functional MRIs, as well as clinical observations. Twelve months later, the patients were re-examined. Surprisingly, about one-third of them “showed brain activity with the presence of some consciousness,” and nine of them recovered a “reasonable level of consciousness.”[3]          

These are patients who might otherwise have missed out on beneficial care, such as pain relief, physical and occupational therapy, and learning how to communicate with the patient.[4] Neurological specialists might not have visited them. In the worst case, medical treatment, including their feeding tube, could have been withdrawn.          

There are several important lessons here. First, medical diagnoses are not infallible. Doctors can be wrong. This warrants humility and caution, especially about diagnoses that affect life and death decisions. Second, science and technology continue to advance, opening up more insights into the mysteries of the brain. That, too, calls for humility and caution about what we know now. Our best assessments can be based on incomplete information, or even flawed assumptions, things revealed by later discoveries. Finally, the PET scan study I mentioned is a small one, and needs to be repeated. But it is encouraging.           

Don’t expect perfection from your doctor. And remember, even technology has its limits.

[1] Martin M Monti, Steven Laureys, and Adrian M Owen, “The Vegetative State,” BMJ 341 (August 2, 2010): c3765.

[2] Keith Andrews, Leslie Murphy, Ros Munday, and Claire Littlewood, “Misdiagnosis of the Vegetative State: Retrospective Study in a Rehabilitation Unit,” BMJ 313, no. 7048 (July 6, 1996): 13.

[3] Johan Stender, Olivia Grosseries, Marie-Aurelie Bruno et al., “Diagnostic Precision of PET Imaging and Functional MRI in Disorders of Consciousness: A Clinical Validation Study.” The Lancet, April 16, 2014. doi:10.1016/S0140-6736(14)60042-8. (Accessed April 22, 2014.)

[4] Andrews, Murphy, Munday and Littlewood.


Everyday Bioethics Audio Commentary Album Art